From f92c90e296211fb3c36df1026597b3387dbe8c48 Mon Sep 17 00:00:00 2001
From: timersha <gilmutdinovtimersha@gmail.com>
Date: Mon, 11 Nov 2024 08:56:09 +0300
Subject: [PATCH] HW2

(cherry picked from commit f59425ac23dea20b40c10dee09b627a1e1068b77)
---
 hw02_unpack_string/.sync          |  0
 hw02_unpack_string/go.mod         |  2 +-
 hw02_unpack_string/unpack.go      | 93 ++++++++++++++++++++++++++++++-
 hw02_unpack_string/unpack_test.go | 18 +++---
 4 files changed, 102 insertions(+), 11 deletions(-)
 delete mode 100644 hw02_unpack_string/.sync

diff --git a/hw02_unpack_string/.sync b/hw02_unpack_string/.sync
deleted file mode 100644
index e69de29..0000000
diff --git a/hw02_unpack_string/go.mod b/hw02_unpack_string/go.mod
index 3b20310..9d8651b 100644
--- a/hw02_unpack_string/go.mod
+++ b/hw02_unpack_string/go.mod
@@ -1,4 +1,4 @@
-module github.com/fixme_my_friend/hw02_unpack_string
+module github.com/timersha/golang-tests/hw02_unpack_string
 
 go 1.22
 
diff --git a/hw02_unpack_string/unpack.go b/hw02_unpack_string/unpack.go
index 41f003d..7b3f3fb 100644
--- a/hw02_unpack_string/unpack.go
+++ b/hw02_unpack_string/unpack.go
@@ -2,11 +2,98 @@ package hw02unpackstring
 
 import (
 	"errors"
+	"math"
+	"strconv"
+	"unicode"
 )
 
 var ErrInvalidString = errors.New("invalid string")
 
-func Unpack(_ string) (string, error) {
-	// Place your code here.
-	return "", nil
+func Unpack(input *[]rune, result *[]rune) error {
+	inputIndex := 0
+	resultIndex := 0
+	backslash := '\\'
+	inputLen := len(*input) - 1
+
+	// validate length
+	if inputLen == 0 {
+		return nil
+	}
+
+	for inputIndex <= inputLen {
+		r := (*input)[inputIndex]
+
+		// starts with digit
+		if unicode.IsDigit(r) && inputIndex == 0 {
+			return ErrInvalidString
+		}
+
+		inputNextIndex := nextIndex(input, inputIndex)
+		nextR := (*input)[inputNextIndex]
+		// finds number
+		if inputLen != inputNextIndex && unicode.IsDigit(r) && unicode.IsDigit(nextR) {
+			return ErrInvalidString
+		}
+
+		// escaped symbol is valid
+		isValidForEscape := unicode.IsDigit(nextR) || nextR == backslash
+		if r == backslash && isValidForEscape {
+			*result = append(*result, nextR)
+			resultIndex++
+			inputIndex += 2
+			continue
+		}
+
+		// escaped symbol is not valid
+		if r == backslash && !isValidForEscape {
+			return ErrInvalidString
+		}
+
+		// repeatedly add rune
+		isDigit := unicode.IsDigit(r)
+		if isDigit {
+			shift := appendRune(result, (*result)[previousIndex(result, resultIndex)], r)
+			resultIndex += shift
+			inputIndex++
+			continue
+		}
+
+		// don't append current rune
+		vl, err := strconv.Atoi(string(nextR))
+		if err == nil && vl == 0 {
+			inputIndex++
+			continue
+		}
+
+		// simple append
+		*result = append(*result, r)
+		resultIndex++
+		inputIndex++
+	}
+
+	return nil
+}
+
+func appendRune(res *[]rune, rn rune, count rune) int {
+	value, err := strconv.Atoi(string(count))
+	if err != nil {
+		return 0
+	}
+
+	for range value - 1 {
+		*res = append(*res, rn)
+	}
+	return value
+}
+
+func nextIndex(sl *[]rune, index int) int {
+	slLen := math.Max(0, float64(len(*sl)-1))
+	nextIndex := index + 1
+	return int(math.Min(float64(slLen), float64(nextIndex)))
+}
+
+func previousIndex(sl *[]rune, index int) int {
+	slLen := math.Max(0, float64(len(*sl)-1))
+	previousIndex := index - 1
+	return int(math.Min(float64(slLen), math.Max(0, float64(previousIndex))))
 }
diff --git a/hw02_unpack_string/unpack_test.go b/hw02_unpack_string/unpack_test.go
index 9799e18..910c546 100644
--- a/hw02_unpack_string/unpack_test.go
+++ b/hw02_unpack_string/unpack_test.go
@@ -17,28 +17,32 @@ func TestUnpack(t *testing.T) {
 		{input: "", expected: ""},
 		{input: "aaa0b", expected: "aab"},
 		// uncomment if task with asterisk completed
-		// {input: `qwe\4\5`, expected: `qwe45`},
-		// {input: `qwe\45`, expected: `qwe44444`},
-		// {input: `qwe\\5`, expected: `qwe\\\\\`},
-		// {input: `qwe\\\3`, expected: `qwe\3`},
+		{input: `qwe\4\5`, expected: `qwe45`},
+		{input: `qwe\45`, expected: `qwe44444`},
+		{input: `qwe\\5`, expected: `qwe\\\\\`},
+		{input: `qwe\\\3`, expected: `qwe\3`},
 	}
 
 	for _, tc := range tests {
+		var res = make([]rune, 0, 100)
 		tc := tc
 		t.Run(tc.input, func(t *testing.T) {
-			result, err := Unpack(tc.input)
+			runes := []rune(tc.input)
+			err := Unpack(&runes, &res)
 			require.NoError(t, err)
-			require.Equal(t, tc.expected, result)
+			require.Equal(t, tc.expected, string(res))
 		})
 	}
 }
 
 func TestUnpackInvalidString(t *testing.T) {
 	invalidStrings := []string{"3abc", "45", "aaa10b"}
+	var res = make([]rune, 0, 100)
 	for _, tc := range invalidStrings {
 		tc := tc
 		t.Run(tc, func(t *testing.T) {
-			_, err := Unpack(tc)
+			runes := []rune(tc)
+			err := Unpack(&runes, &res)
 			require.Truef(t, errors.Is(err, ErrInvalidString), "actual error %q", err)
 		})
 	}